Taking place after the events of Kamen Rider Decade episode 15, under the impression that they saved the World of Den-O, Tsukasa Kadoya and company begin their journey to the World of Kabuto when they are halted by Sieg who presents them a manuscript that detailed the legendary Oni Conquest with Momotaros’ image on it. As this occurred, the Tarōs mysteriously vanish from the DenLiner as they are about to help Kotaro Nogami out with the true threat to their world. Meanwhile, in the year 1980, a boy named Yu encounters Mimihiko and then Yu is possessed by Deneb who gets him away from the Gelnewts before New Den-O arrives to cover his escape. Deneb then brings Yu to Ryotaro, revealing Mimihiko to be one of the Oni of legend and is searching for the Trump Stone (切り札の石Kirifuda no Ishi?) which Yu possesses.